Corrosion inhibitor



Jan. 12, T. GIBBS CORROSION INHIBITOR Filed Jan. 6, 1949 J Q ZCAMM ATTORNEYS Patented Jan. 12, 1954 CORROSION INHIBITOR Lloyd T. Gibbs, Tulsa,

Aldrich Pump Compan poration of Pennsylva Okla, assignor to The y, Allentown, Pa., a cor nia Application January 6, 1949, Serial No. 69,451

2 Claims.

This invention relates to the inhibition of corros on in pumps and is particularly concerned with preventing corrosion of the parts of pumps which are in contact with corrosive substances.

I am aware that it has heretofore been proposed to protect metallic structures from thecorrosive action of polar fluids by permitting the fluid to come in contact w th a mass of a metal higher in the electrochemical series than the metal to be protected, the mass being in electrical contact with the metal to be protected.

This technique, in the final analysis, consists in establ shing a galvanic battery whose electrolyte is the corrosive working fluid, whose cathode is represented by the metal working parts to be protected, and for which an anode is supplied. in the form of a mass of metal higher in the electrochemical series than the metal to be protected. It is thus necessary that the anodic material be electrically interconnected with the metal parts to be protected, and that it be immersed in the working fluid. It is also desirable to locate the anode as close as is conveniently possible to the parts to be protected in order to shorten both the external metallic circuit and the internal electrolytic circuit.

The application of this technique to apparatus in which the working fluid is turbulent presents special problems and this is particularly so in the case of pumps, wherein it is necessary to take into consideration the necessity for maintaining clearance between parts having movement relative to one another. The problem of preventing corros on in pumps is still further complicated by the fact that the anodic material is preferably associated with a passage communicating directly with moving parts of the pump, for, should a mass of anodic material be loosened from a position in such a passage, it may be impelled directly into the working parts of the pump and quite possibly result in serious damage.

It would at first appear that a pump could be protected against corrosive attack by the Working fluid by securing a relatively large mass of anodic metal to an interior surface of one of the pump passages, for example, by bolts or screws. I have found, however, that this is unsatisfactory, because the attack of the fluid upon the less noble metal is concentrated on the point of attachment to the metal to be protected, with the consequence that any such mechanical connection is soon destroyed, freeing the mass of metal and paving the way for destruction of the pump by occlusion of the. mass of anodic material between two relatirely moving parts.

According to the present invention, I support the less noble metal, preferably in the form of pellets or small bars, in an enclosure, which enclosure is physically supported by and in electrical connection with the metallic structure of the apparatus to be protected.

The enclosure must be capable of physically supporting the anodic material and also include means for-completing the electrical circuit between the anodic material through the pump body to the parts to be protected, and, hence, must be fabricated at least in part from a conductive metal. Inasmuch as it is contemplated that the supporting assembly itself should have a useful life comparable to the life of the pump itself, it should not be fabricated from the anodic material but is preferably formed from a material lower in the electrochemical series, and, desirably, from a metal similar in electrochemical properties to the metal to be protected. Since in most cases pumps include parts fabricated from iron and its alloys, or copper and its alloys, or both, the supporting assembly may most conveniently be made of such material.

The support is provided with a number of openings, providing for passage of ions through the fluid space within the pump to the parts to be protected. The maximum size of these apertures is controlled by the necessity for maintaining particles exceeding a certain size within the basket, while the minimum dimension of the apertures is determined by the necessity for per-- mitting adequate circulation therethrough.

I have illustrated my invention as applied to an inverted vertical reciprocating pump of a known type, although it is to be understood that the invention is applicable to any pump comprising parts which are subject to corrosion by the attack of polar solutions.

How the invention is accomplished will appear more fully upon referring to the detailed description herein-below and the drawings, in which:

Figure l is a vertical sectional View of a pump incorporating a corrosion inhibitor according to v the present invention;

Figure 2 is a sectional view on an enlarged scale of the corrosion inhibitor of Figure l; and

Figure 3 is a plan of the assembly of Figure 2.

The pump illustrated in Figure 1 is an inverted vertical reciprocating pump of a type employed in pumping fluids at relatively high pressure, a typical use for such a pump being in back pressuring operations in the oil fields which involves the forcing of brines into the ground aronndan. oil. Well to aid in forcing the oil into the well. The brines are obtained from the well and are generally characterized by relatively high concentration of sodium chloride and other salts which render them hi hly corrosive to ferrous and cupreous metals and alloys.

The pump disclosed in Figure 1 comprises a crankcase section generally indicated at It, and a pump body l l which may be machined from a steel forging, and comprising a cylinder 52 having a piston i3 therein adapted to be reciprocated by a pair of tension rods M which interconnect the top of the piston with the crosshead 15.

The pump body ii is also characterized by an intake passage It, a discharge passage H disclosed generally parallel thereto, and a vertical valve chamber is intersecting passages 56 and I? and containing intake and discharge valves as generally designated at It and 223, respectively. The valve parts may be formed of iron alloys such as steel, or, alternatively, of alloys of copper, for example, bronse.

Cylinder l2 and valve chamber 18 interconnected by horizontal bore 25 which is out out during the course of manufacture from the left side 22 of the pump body H, as viewedin Figure 1.

As may be seen in Figure 1, vertical valve chamber is and horizontal bore i, together with cylinder i2, comprise a working which is interconnected with intake passage l8 and discharge passage l? by valves is and 12% respectively. When the pump is in operation, there is intermittent upward motion of working fluid from intake passage l into the working space, recipro eating motion of working fluid between cylinder 52 and valve chamber and intermittent upward movement of working fluid through valve 225} into discharge passage El.

Accorangly, a galvanic anode disposed in the intake line, in intake passake it, within the working space of the pump, or even in the discharge passage or discharge line, will be protective of all pump parts in contact with the working fluid, and where the pump is in substantially continuous operation, the inhibitor anode may be located at any of these points.

However, when the pump is shut down, under which condition both valves it and 2d are closed, the working space is effectively cut off from both the discharge and intake passages. During the down period, corrosion may occur in the working space, and, accordingly, where it is contemplated that pump operation will be intermittent, I locate the inhibitor anode assembly at a point where the anode in contact with the fluid in the working space. In some installations it will be desirable to protect the intake and discharge passages instead of or in addition to the working space. In other installations, as for example in valveless pumps, the location of the inhibitor assembly will not be critical.

It should also be pointed out that in multicylinder pumps, where each cylinder is separately valved, it is necessary to install an inhibitor assembly in each working space when working space protection is desired.

1 have illustrated in Figure 1 the application of an inhibitor assembly to the working space of the pump, the assembly illustrated being made in the form of a basket 23 and cover plate 2% disposed in and over the left end of horizontal bore 2!.

Referring now to Figure 2, it will be seen that basket 23 comprises a wall 25 having therein a number of perforations 25a.

Basket 23 is also characterized by an annular 4 flange 26 adapted to engage a complementary seat 2'! on pump body H, as may be seen in Figure 1. A gasket 26a is interposed between flange 26 and seat 21.

The barrel portion 23 of basket 23 is tapped to receive a pair of screws 29 (see Figure 3) for securing the same to cover plate 2 Cover plate 26 in turn is provided with a plurality of holes 311 by means of which the cover plate and basket assembly are secured to pump body II by studs or bolts 3!. A second gasket 24a seals the joint between cover plate 2 3 and basket 23.

The size of the apertures 25a in wall 25 of basket 23 is determined to some extent by the nature of the apparatus which it is sought to protect, since the apertures must be large enough to permit circulation of working fluid into and from the interior of the basket and small enough to retain within the basket particles of material large enough to cause damage to the apparatus if they should escape. In the pump illustrated in Figure 1, I have found that apertures not larger than in diameter, and preferably about are suitable, the upper limit in this case being established by the clearance limitations in the cylinder and valve mechanism of the pump. It will be understood, of course, that in pumps having larger clearance somewhat larger apertures might be used, although the use of larger apertures necessarily entails the possibility of losing correspondingly larger particles of anodic material.

In the embodiment illustrated herein, the lower limit on the size of the apertures is established simply by considerations of convenience in manufacture, since the basket is formed by machining a forging and. the apertures must be formed by drilling. Holes smaller than are somewhat more troublesome to drill and, since it has been found that this size is adequate, the invention has been so illustrated.

It will be understood that other methods of manufacture and other environments may render it desirable to reduce the size of the apertures, and this may be done so long as provision is made for sufficient circulation of working fluid to and from the interior of the basket.

Basket 23 is charged with particles of metals less noble than the metals to be protected. The highest single electrode potential of any metal commonly employed in pump manfacture is that of iron, and, accordingly, the anode material must be selected from among the metals whose electrode potentials are higher than that of iron. In addition, the metal selected for the anode should be comparatively easy to handle, and should be one which forms a relatively insoiubl hydroxide. I have found that magnesium, which has a single electrode potential of +15% (referred to a normal hydrogen electrode) is especially suitable, although it will, of course, be understood that others of the less noble metals may also be used, for example, zinc and alinni. num. The metal may be used in the form or pellets,,rods, wire, or other conveniently handled shapes. In the practice of the invention, I have found that pieces of magne ium rod oi about .65" diameter give completely satisfactory results, and I have accordingly illustrated the basket Figures 1 and 2 as being charged with pieces 32 of such rod.

According to the invention, when a pump is employed under circumstances wherein it is contemplated that corrosion of pump parts will 0cour, a basket 23 is charged with particles 32 of anodic material, cover plate '24 is secured to the basket by screws 29, and the cover plate in turn installed in the pump in the manner above described by means of bolts 3|.

When the pumping operation is commenced and the pump passages are filled with the corrosive working fluid, the pump parts comprising nobler metals, and the less noble metal in the basket become respectively the cathode and anode of a galvanic battery whose electrolyte is the corrosive working fluid, the electrical circuit between the cathode and anode being completed through the pump body II and basket 23. The galvanic attack on the anodic material begins immediately, and, in the case of a pump which has not previously been equipped with my corrosion inhibitor assembly, the corrosive action is at first most vigorous. As the process continues,

however, a dull, dark coating forms on the interior surfaces of the pump parts, and thereafter the rate of attack on the anode apparently decreases. I am uncertain as to the exact nature of the coating which is deposited on the cathodic surfaces, but believe that it consists essentially of the relatively insoluble hydroxides of the material being used as an anode. Whatever its nature, it is apparently this coating which decreases the vigor of the galvanic dissolution of the anode.

When the inhibitor basket has been assembled and the initial activity which has just been described has occurred, the protective action of the galvanic battery continues at a decreased rate until the anodic material has been entirely consumed. It is thereafter only necessary that periodic inspection be made to ascertain the condition of the anode, which may readily be accomplished, according to my invention, merely by removing the basket assembly 23 and examining the contents.

It will be understood that the invention contemplates modifications of the anode carrier to conform with the requirements of installation in other parts of the pump and in different types of pumps. In every case, however, the assembly includes a screen member providing for fluid communication with the anodic material and serving to prevent migration of the anodic material, and means for physically supporting the anodic material and for establishing electrical interconnection with the metallic parts to be protected.

Depending upon the volume of fluid being pumped and the concentration and nature of the polar substances therein, the anodic material will last for considerable periods. For example, in a typical installation in a pump having a capacity of 6000 gallons per hour, operating 24 hours per day, I have found that a single charge of magnesium will protect the pump for a period of from one to six months. The initial charge is generally exhausted in a matter of three or four weeks, but successive charges extend protection to the pump for gradually increasing periods reaching, in the example under discussion, a maximum of six months. [So long as the anodic material is replenished at intervals corresponding to the rate of dissolution, the pump may be protected against corrosion indefinitely. The value of this protection may be appreciated upon consideration of the fact that under the conditions of operation just above referred to, corrosive conditions without the use of my inhibitor assembly were so acute as to require the complete fluid end of the pump to be discarded after a period of from six months to two years.

I claim:

1. In a pump adapted for use with corrosive polar fluids and comprising a metallic portion defining a passage for such fluid and a port from said passage to the exterior of the pump, a metallic inhibitor assembly comprising a basket portion extending into said port and in metallic contact with said metallic portion and having a flanged portion projecting over the edge of said port exteriorly of the pump and removably secured to said metallic portion, said basket being in part defined by a perforate wall dividing the interior of the basket from said passage, and a closure member for the basket, seating against the flanged portion thereof, said basket containing particles of metal anodic to said metallic portion.

2. In a pump adapted for use with corrosive polar fluids and comprising a metallic portion defining a passage for such fluid and a port from said passage to the exterior of the pump, a metallic inhibitor assembly comprising a basket portion extending into said port and in metallic contact with said metallic portion, the basket portion being removably secured in said port to said metallic portion and having an end exposed exteriorly of the pump, said basket being in part defined by a perforate wall dividing V the interior of the basket from said passage, and

a member closing the exposed end of the basket, said basket containing particles of metal anodic to said metallic portion.

LLOYD '1". GIBBS.

References Cited in the file of this patent UNITED STATES PATENTS 

2. IN A PUMP ADAPTED FOR USE WITH CORROSIVE POLAR FLUIDS AND COMPRISING A METALLIC PORTION DEFINING A PASSAGE FOR SUCH FLUID AND A PORT FROM SAID PASSAGE TO THE EXTERIOR OF THE PUMP, A METALLIC INHIBITOR ASSEMBLY COMPRISING A BASKET PORTION EXTENDING INTO SAID PORT AND IN METALLIC CONTACT WITH SAID METALLIC PORTION, THE BASKET PORTION BEING REMOVABLY SECURED IN SAID PORT TO SAID METALLIC PORTION HAVING AN END EXPOSED EXTERIORLY OF THE PUMP, SAID BASKET BEING IN PART DEFINED BY A PERFORATE WALL DIVIDING THE INTERIOR OF THE BASKET FROM SAID PASSAGE, AND A MEMBER CLOSING THE EXPOSED END OF THE BASKET, 